Computer technology has expanded rapidly in recent times and in this country millions of individuals now have ready access to computer terminals through which they can communicate with data networks. A very large portion of actual computer use involves the user accessing, manipulating, updating, or utilizing massive amounts of data in real time. In the vast majority of cases, the user has relatively limited knowledge or understanding of the complex programs and hardware system, and most users find it most convenient to manipulate the data in highly visible form.
Among the mechanisms by which a computer user can call up data, change display modes and make changes to the displayed data are keyboards, light pens, small hand-operated devices known generally by the term "mouse" and, most recently, touch sensitive screens or panels.
In principle, touch sensitive data input devices are obtainable in a variety of forms, and may operate by any of a variety of mechanisms. These include devices wherein, typically, the touch of a user's finger at a point on a touch sensitive surface causes interruption of light beam arrays, change in local capacitance, change in local resistivity by piezoelectric effect, and by contact between adjacent closely-spaced electrical conductors aligned in mutually orthogonal directions.
Successful embodiments of the last mentioned approach typically comprise two flexible membrane-like elements disposed in face-to-face relationship and separated from each other by a slight air gap. The elements typically are optically clear flexible polymeric sheet-like elements which are normally separated by small bumps on one or the other of the adjacent surfaces. A clear stiff backing panel, e.g., a glass sheet, is located behind the rear element to provide support when a user applies force to the front surface of the front element during use of the device. An operator pressing on the outer one of the elements will cause both elements to touch locally, to form a local contact area which can be detected by sensitive circuitry connected to thin, narrow, highly conductive layers disposed on the two adjacent contactable surfaces and connected to the computer system. Electrical current flow at a local contact point is translated into the location of the contacting conductors on the screen. Such spatial discrimination and the resultant signals can be utilized with a computer program for the manipulation of data visibly displayed through the two optically clear adjacent and contactable elements.
A major problem in manufacturing such a device from the most suitable materials is that due to ambient temperature changes in use the stiff transparent backing plate expands or contracts at a significantly different rate then either the material surrounding it or the clear flexible front and rear elements that it supports itself. This differential expansion can cause deformation, e.g, bending of the backing plate, wrinkling of the flexible elements and the like, and prevent adequate sealing against dust, moisture and other pollutants that may get into the sensitive zone between the flexible elements.
Accordingly, a need exists for a touch sensitive data input device that accomodates differential thermal expansion between adjacent coacting elements, provides effective sealing against pollutants in the environment and is readily attached to the data display unit with which it is used.